1. Field of the Invention
This invention relates to heat-curing expanding mouldings based on solid polybutadiene rubbers and vulcanizing agents of which the vulcanizing agent is free from elemental sulfur. The invention also relates to a process for the production of these mouldings, to their use for bonding and/or sealing metal parts and to a process for the bonding of solid surfaces, more particularly metal parts for use in vehicle construction.
2. Discussion of the Related Art
The metal parts bonded and sealed in car manufacture, particularly in car bodies, are often untreated. The adhesives/sealants used are cured at a later stage in the paint drying ovens. Before this, the bonded and sealed parts pass through cleaning, phosphating and dip-priming stages. Under the effect of the treatment chemicals used in these stages, the adhesives or sealants can be removed from the joints. Various procedures have been developed to meet these requirements, including for example thermal/inductive precuring of low-viscosity paste-form adhesives/sealants, the use of adhesives in the form of solvent-containing compositions or hotmelts, as two-component products or even as mouldings which are generally applied by hand and which are surface-tacky at the time of application. These mouldings may be present in tape form or as round cords, stampings or profiles as any cross-section.
DE-A-34 45 325 describes surface-tacky mouldings, more particularly sealant profiles, which are produced from plastisols based on PVC and/or polymeric methacrylic acid esters and/or ethylene/vinyl acetate copolymers. However, these mouldings are in need of improvement. For example, they only adhere to EC-primed metal so that, for this reason alone, they cannot be used at the "white shell" stage, i.e. cannot be applied to the non-pretreated oil-covered metal panels. Since it is known that plastisol compositions retain their thermoplastic character, even after gelling, corresponding bonds or seals lose their mechanical strength on exposure to heat.
To overcome the last two technical problems, heat-curing mouldings based on rubber have been in use for several years. They generally consist of a mixture of liquid and optionally solid rubbers based on polyolefins, more particularly on diene homopolymers and copolymers. As their curing system, these rubber mouldings contain a vulcanization system based on elemental sulfur and optionally accelerating vulcanization auxiliaries. In principle, the composition of these mouldings is similar to that of the pumpable paste-form products described, for example, in JP-A-93059345 or in DE-A-38 35 740. Other examples of heat-curing, expanding and non-expanding adhesives based on sulfur-vulcanizing rubber adhesives in solvent-containing or solvent-free form are described in EP-A-476 224, EP-A-643 117 and in hitherto unpublished DE-A-195 18 673. JP-A49099643 describes readily extrudable vulcanizable rubber compositions which contain Li-catalyzed butadiene rubber, i.e. rubber with a high trans-1,4-content, and of which the vulcanization system consists of elemental sulfur and p-benzoquinone dioxime. In addition, these compositions have a very high content of carbon black. For these reasons, the rubber compositions in question are unsuitable for the production of the heat-curing expanding mouldings according to the present invention, i.e. are unsuitable as white shell adhesives and sealants in car production.
Heat-curing expanding mouldings based on solid and, in some cases, even liquid rubbers and vulcanizing agents containing elemental sulfur belong to the prior art although, as far as applicants are aware, they have not been published in patents. These known mouldings generally consist essentially of a mixture of solid butyl rubber, precrosslinked solid butyl rubber, solid natural rubber and extender oils, fillers, tackifying resins, pigment black, coupling resins and a vulcanization system based on elemental sulfur and optionally organic expanding agents.
Although the heat-curing mouldings just mentioned are already wide-spread in practice, they are in need of significant improvement in certain respects:
The cured products have a typical "rubber odor" which is presumably attributable to the elemental sulfur used in the vulcanization or crosslinking system; this odor is particularly unpleasant during curing. PA1 In the untreated state in which they are supplied, the preformed/dimensioned profiles/stampings for manual application are supposed to have minimal rubber-elastic resilience and to be readily formable so that they may be adapted without significant effort to the metal parts to be joined and completely fill the gaps with ease. PA1 Excessive resilience of the mouldings should not result in unfavorable tensions and deformation of the metal parts being "fixed" in the curing process. PA1 A soft, elastic foam with a continuous outer skin should be formed after curing. PA1 one or more solid rubbers based on polybutadiene or copolymers thereof, PA1 vulcanizing agents which are free from elemental sulfur, vulcanization accelerators, catalysts, PA1 fillers, PA1 tackifiers and/or coupling agents, PA1 blowing agents, PA1 extender oils, PA1 antiagers, PA1 flow aids.
The properties mentioned above are also particularly important in the so-called sandwich bonding of metal parts with underlying reinforcing frames or supports so that the deformation of the metal parts thus bonded is reduced to a minimum. This is particularly important for the large-surface metal parts of a car body of which the outside remains visible so that the optical impression of the high-gloss paint surface of the finished body is not marred by the so-called "read-through" effect.